Hydraulic master cylinder



March 25, 1952 J. T. RlssE HYDRAULIC MASTER CYLINDER Filed Feb. 16. 1951 INVENTOR.

Patented Mar. 25, 1952 UNITED STATES PATENT oFF-ICE 2,590,430 nenn-autrev MASTER CYLINDER .lohn T. Risse, Eldora Iowa Application February 16, 1951, Serial. No,.,211,327' (ci. ca -54.6)

3 Claims.

This invention relates to new and useful. imprcvements and structural renements in hydraulic master cylinders, and the principal object of the invention is to provide a cylinder of the character herein described which is capable of two-stage operation by first exerting relatively low pressure in the hydraulic system by displacement ofa relatively large volume of fluid, and thenl exerting relatively high pressure in the hydraulic -system by displacement of a relatively small amount of uid, this facilitating enicient, progressive control of a hydraulic device or devices which the master cylinder actuates.

Some of the advantages of the invention reside in itssimplicity of construction, dependability of operation and adaptability for use in hydraulic systems of different types.

Primarily, the invention is intended for use in hydraulic brake systems' of automobiles, etc.,v but obviously it may -be utilized in other environments.

With the above more important objects and features in view and such other objects and features as may become apparent as this specication proceeds, the invention consists essentially y in the construction and arrangement of parts as shown in the accompanying drawing, in which:

Figure 1 is a longitudinal sectional View of the hydraulic master cylinder in its initial position;

Figure 2 is a longitudinal sectional view, similar to that shown in Figure 1, but illustrating the master cylinder in its position representative of an ultimate; and

Figure 3 is a transverse sectional view, taken substantially in the plane of the line 3-3 of Figure 2.

Like characters of reference are employed to designate like parts in the specification and throughout the several views.

Referring now to the accompanying drawing in detail, the invention consists of a hydraulic master cylinder which is designated generally by the reference character Iii and embodies in its construction an elongated, substantially cylindrical housing I2 pro-vided with end walls I4, I6, While a hydraulic uid reservoir I8 is provided on top of the housing l2 adjacent the end wall I6, as shown.

A cylindrical housing extension 20 is provided at the outside of the end wall I6 coaxially with the main housing l2, the extension 20 having an outer end Wall 22, The end walls I4, I6 and 22 are preferably of a greater diameter than the housing I2 and extension 2H, and a plurality of tie rods 24 extend through marginal edge por- What may be called av low pressure piston 30,

of a relatively large diameter, is slidable i-n the housing I2, and a portion. of the housing I2 be.- tween the piston 30, and the end wall I6 affords a low pressure fluid chamber 32 which communicates with the reservoir I8; through the medium of a passage 34 which is uncovered by the piston when the latter is in its initial position as sho-wn in Figure 1.

A reciproca-ble actuating rod 3B extends slidably through the end wall I4 into the housing I'2 and is also slidable in a bore 38 of the piston 3D, the inner end portion of the rod 36 having a frusto-conical extremity and constitutingl what may be called a high pressure piston 4l)v which is of a substantially smaller diameter than the piston 39.

The end wal-l I6 is jprovided with a passage 42, counterbored, as at 44, which passage connects the fluid chambers 26, 32, andwhat may be referred to as a checkvalving seal 46 is mounted in the counterbore 44 and has la truste-conical, apertured center portion 48 which is directed toward the chamber 26, as shown.

When the actuating rod 3,6 is in its initial position, as shown in Figure. 1, the high pressure piston 49 extends partly into the seal 46, but sufficient space exists between the piston and the seal portion 48 to permit flow of uid from the chamber 32 into the chamber 2.6, or vice versa.

A transverse stopV pin 50 is provided in the rod 36 and projects laterally from the rod sov as to abut. the inner surface of the end wallv I4 when the rod 3B is in its initial position, .as shown in Figure 1, a washer 52 being positioned on the rod 36 at the inside of the pin 50 to abut one end of a compression spring 54. The other end of this spring abuts a washer 53 which, in turn, abuts the piston 30, it being noted that a shoulder 58 is provided intermediate the ends of the rod 36, which shoulder abuts the washer 56 when the device is in its Ainitial position as shown in Figure 1.

Finally, it is to be observed that a compression spring 60, which is substantially weaker than the spring 54, is interposed between the piston 30 andthe end wall I6.

Having thus described the construction of thc invention, the operation thereof will now be explained.

Assuming the device to be in its initial position as shown in Figure l, the piston will uncover the passage 34 so that the hydraulic system may be filled by fluid from the reservoir I8, the piston 40 being spaced from the seal portion 43, so that communication in both directions is maintained between the chambers 26, 32 to facilitate equalization of fluid `pressure therein.

Assuming, now, that the actuating rod 36 is slid tc the right, that is, in the direction of the arrow 62, the piston 30 will first cover the passage 34 while at substantially the same time the piston 4D will frictionally engage the portion 43 of the seal 46, and as the piston 30 continues in its movement to the right, uid in the chamber 32 will be expelled into the chamber 25 by being forced between the piston 40 and the frustoconical portion 48 of the seal 46, whereby a relatively large Volume of fluid will be displaced at relatively low pressure to initially actuate a hydraulic device or devices connected to the duct It should be explained at this point that the piston 3i), which is not secured to the rod 36, is slid to the right only by the action of the compression spring 54 Awhich is possible only when the rod 36 itself is slid to the right so that the shoulder 58 of the rod may recede from the washer 56, as illustrated in Figure 2. Of course, the spring 54, being stronger than the spring E50, overcomes the pressure of the latter spring in forcing the piston to the right, as aforesaid.

When a suflicient amount of fluid has been displaced under low pressure to initially actuate a fluid pressure-responsive device connected to the duct 23, and when that low pressure iiuid displacement is incapable to further actuate that device so as to overcome whatever load may be placed on the latter, the low pressure piston 3u will come to a stop, such as for example, at a point illustrated in Figure 2, but sliding of the rod 35 in the direction of the arrow 62 will project the high pressure piston 40 into the high pressure fluid chamber 2B, thus furnishing a small volume displacement of uid at proportionately higher pressure to further actuate the fluid pressure-responsive device to which the master cylinder is connected.

It will be apparent from the foregoing that in this manner the operation of the hydraulic system is in two stages, namely, a low pressure, high volume displacement stage, and a high pressure, low volume displacement stage, and it is to be noted that once the high pressure piston 40 comes in engagement with the portion 48 of the seal 4E, fluid may pass through the sealportion 48 from the chamber 32 into the chamber 26, but not from the chamber 2S into the chamber 32. This is assured by the frustoconical configuration of the seal portion 48 which frictionally engages the piston 4i).

When the actuating rod 36 is slid to the left, that is, to the initial position shown in Figure 1, the spring 50 will counteract the resiliency of the spring 54 in sliding the piston 30 to its initial position, this representing the sole function of the spring 6U. When that occurs, the high pressure piston 4B will be spaced from the seal portion 48 and the fluid under pressure in the chamber 26 and duct 28 will be able to return into the chamber 32 to effect equalization.

It is believed that the advantages and use of the invention will be clearly understood from the foregoing disclosure, and, accordingly, further description thereof at this point is deemed unnecessary.

Having described the invention, what is claimed as new is:

l. In a hydraulic master cylinder, the combination of an elongated housing having iirst and second end walls, a housing extension provided at the outside of the second end wall and affording a high pressure fluid chamber having an outlet port, a relatively large low pressure piston slidable in said housing, a portion of the housing between said piston and said second end wall constituting a low pressure fluid chamber, said second end wall being provided with a fluid passage connecting the high and low pressure chambers, a reciprocable actuating rod extending slidably through the first end wall into the housing and having its intermediate portion slidable in said low pressure portion, a compression spring provided in the housing for urging the low pressure piston toward said passage when said actuating rod is slid inwardly, a check-valving seal provided in said passage, the inner end portion of said actuating rod constituting a relatively small high pressure piston engageable with said seal and projectable into the high pressure chamber when said actuating rod is slid inwardly and the low pressure piston is stationary, and a second compression spring provided in said housing for urging the low pressure piston to its initial position when the actuating rod is slid outwardly, a shoulder provided intermediate the ends of said actuating rod, a collar slidable on said rod, and a stop provided on said rod adjacent said rst end wall, one end of the first-mentioned spring abutting said stop and the other end thereof abutting said collar whereby to urge the latter against said shoulder, the second-mentioned spring urging the low pressure piston against said collar.

2. The device as defined in claim l wherein the first and second-mentioned springs are disposed at opposite sides of the low pressure piston, the second spring being substantially weaker than the first spring.

3. In a master cylinder, a housing having a first fluid chamber and a uid reservoir cornmunicating therewith, a housing extension having a second uid chamber in communication with said rst chamber and having an outlet port therein, a large piston slidable in said housing and having an axial bore therethrough, a small piston being slidably received in said bore, a shoulder intermediate the ends of said small piston, a stop on said small piston spaced from said shoulder, a collar slidably received on said small piston and initially abutting said shoulder and one end of said large piston, a compression spring surrounding said small piston and having one end abutting said stop and the other end abutting said collar to initially urge the collar against said shoulder and said large piston, a wall separating said first and second chambers and having a central aperture therein, a check-valving seal in said aperture, the inner end of said small piston engaging said seal and being projectible therethrough into said second chamber when the pressure of the uid in the first chamber equalizesv the pressure exerted by the compression spring on the large cylinder whereby the rst chamber becomes a low pressure chamber and the second cylinder 6 becomes a high pressure chamber, a second spring interposed between said separating wall UNITED STATES PATENTS and the other end of said large piston to urge Number f Name Date the large piston to its initial position with respect 763,833 More@ une 23, 1904 to the small piston as the small piston is res 1,935,583 Tai-,ter Dm 25) 1934 tracted from the second uid chamber. 2,102,834 Carroll Dea 21J 1937 JOHN T- RISSE- 2,106,304c McGee Jan. 25, 193s 2,373,679 Hawley Apr. 17, 1945 REFERENCES CITE@ 2,531,705 Schultz Nov. 28,1950

The following references are of record in the o le of this patent: 

